1. Field of the Invention
The present invention relates to a power tool such as an electric hammer and more particularly, to a technique of reducing and alleviating vibration in a power tool.
2. Description of the Related Art
A known power tool such as an electric hammer generally includes a driving motor, a driver driven by the driving motor to reciprocate and a tool bit. The known electric hammer linearly drives a driven-side member, such as a striker by utilizing the pressure fluctuation of air within the power tool. Such air is compressed by a reciprocating movement of the driver. When the driven-side member is linearly driven, the tool bit is also linearly driven, so that the tool bit performs a predetermined operation.
In the known electric hammer, the fluctuation of air pressure for driving the tool bit may cause vibration in the electric hammer. That means the driver linearly drives the driven-side member by the pressure of the compressed air, and the driven-side member drives the tool bit. At this time, typically, all of the driving force of the driven-side member is not turned into a driving force of the tool bit. In many cases, part of the driving force of the driven-side member is turned into repulsion that the driven-side member receives in a direction away from the hammer bit. In such a case, the driven-side member may retract at high speed toward the driver. As a result, undesired compression of air may occur and cause undesired vibration toward the rear side of the power tool or toward the user holding the power tool.
As an example of measures for reducing vibration in a power tool, Japanese non-examined laid-open Utility Model Publication No. 51-6583 discloses a technique of reducing vibration using a counter weight. The counter weight reciprocates in a direction opposite to the striker. In this manner, vibration caused in the electric hammer, particularly in the axial direction of the tool bit, can be effectively reduced. However, the counter weight may not always effectively reduce vibration caused by air fluctuations within the electric hammer.